I agree with you but as an owner of a DXRacer chair for the past 10+ months, I can safely say that it does promote a better body posture due to its design that wraps around your body. That is why you must buy the right chair size for yourself and that is why there are many versions of DXRacer chairs per say.
I can tell because I've been slouching a lot in the office vs when I'm at home with this chair.
As for durability wise, it has not started creaking or anything like that. The cushion is still comfortable and it doesn't look like it has sinked in due to wear on the cushions. So ups to that.
As for concerns about heat, some reviewers mention that the seats allows your butt to breathe or something along the line.
For my own experience, yes, Singapore is hot but my butt doesn't feel hot after a long session on it. It is only slightly warm that it has been quite unnoticeable for me especially when wearing shorts where you'll have a more direct contact to the seats.
Comparing the leather that they use for the chair to that of my headphones, I would say I sweat more on my ears than I do on this chair due to how it allows your body to breathe through it as compared to the headphone's leather.
Give it a try on any kind of gaming chairs like maybe our local SecretLab ones which offers value for money plus directly supporting our local enterpreneurs. $399 is reasonable compared to my DXRacer chairs which I bought at $622.96 after GST tax I think which were not included in the price that X-treme Solution promoted at.
At first, you'll feel out of place since the chair really changes your body posture from the first use itself that you'll feel out of place from how you normally sit in an office chair but you'll feel right at home with this chair and really start to appreciate its benefits over time as compared to your office chairs which promotes slouching and not to mention, a lot more warmer butts at times.